Justification:
Listed as Critically Endangered because it is known only from one location: Santa Catalina Island in the Gulf of California, Mexico. The species' highly restricted range, the recent past presence of feral cats, the persecution for illegal trade, the killing by occasional encounters with visitors to the island and the rubbish left by them; its vulnerability caused by the fact that 70% of its diet is composed of the only rodent species on the island, all qualify it for the Critically Endangered category.

It was formerly a common species, but has probably declined, principally due to over-collecting. Abundance data gathered between 2003 and 2004 fluctuated between 0.23 (one snake every four person-hours) in June to 2.11 (two snakes per person-hour) in August (H. Avila-Villegas pers. comm.).

The island topography is composed of rocky hillsides separated by wide and narrow sandy arroyos (dry creeks) bearing the typical Sonoran Desert vegetation. This species occurs mainly in heavily-vegetated arroyos, but can also be found on rocky and scrubby hillsides, beneath roots and rocks or even in open areas of sandy soils. It is mainly nocturnal and can be easily found and caught. Most of its diet (70%) is composed of the endemic mouse Peromyscus slevini, the only ground mammal species on the island.

The main threat to this species is the loss of individuals by killing and illegal collection. "Pit fall" traps have been found on the island, and some fishermen have observed people collecting reptiles in bags. Other fisherman have allegedly taken people to the island to collect the species (what they get paid equals their profits in a week of hard work fishing). Santa Catalina Island is home to 10 reptile species, of which seven are endemic (Grismer 2002). Insular endemic species are the most wanted in the illegal trade market, hence, are the more threatened (Mellink 1995). Its passive behaviour makes it easy to catch or kill. Population declines of its main prey, P. slevini is also an important threat. A population of feral cats formerly invaded the island. G. Arnaud and Hector Avila-Villegas observed several remains of C. catalinensis in the scats (H. Avila-Villegas pers. comm. 2007). These cats were eradicated in 2002 (J. Donlan pers. comm. to H. Avila-Villegas).

Although cats have been eradicated from the island, there is a need to ensure that they do not recolonize Isla Santa Catalina. There is a need to monitor populations and to prevent over-collection of this restricted range species.

Grismer, L.L. 2002. Amphibians and Reptiles of Baja California, Including its Pacific Islands and the Islands in the Sea of Cortés. University of California Press, Berkeley and Los Angeles, California.